The invention is related to the field of magnetoelastic torque sensors and, in particular, to an integrated, two-channel, magnetoelastic torque sensor.
Measurement of torque is useful in a diverse range of automotive and industrial fields. Torque is one of the two fundamental physical quantities required to analyze rotating drive mechanisms. The other physical quantity is the speed of rotation. For example, the torque being transmitted by an automotive driveshaft can provide a wealth of information about the performance of the powertrain and the chassis of the vehicle. Torque measurements could also be valuable in quantifying and analyzing transmission efficiencies. In the analysis of existing torque sensing technologies, it has been concluded that in the automotive field a torque sensing system requiring neither components attached to nor functionally in contact with the shaft would be desirable. Magnetoelastic torque sensors appear to meet these requirements.
Magnetoelasticity is the term used to describe the interactions found in many materials between magnetic properties and elastic properties. Magnetoelastic torque sensor technology operates on the specific manifestation of magnetoelastic termed the Inverse Wiedemann Effect in which a magnetic field can be distorted to arise in the space around a torsionally stressed member. In particular, circularly polarized bands of a magnetoelastically active shaft material creates a magnetic field that in intensity and polarity is a near perfect linear analog of the torque transmitted. No excitation power other than a mechanical torque is required to create this magnetic field, and only a magnetic field detector is required to detect the magnitude and rotational direction of the applied torque.
This invention is a dual-channel magnetoelastic torque sensor having an array of saturable core magnetic flux detectors. The flux detectors detect the magnetic field generated by a pair of oppositely polarized magnetoelastic bands provided on a shaft, such as the drive shaft of an automobile vehicle. The array of saturable core magnetic flux detectors consists of two pairs of diametrically opposite flux detectors. Each pair of diametrically opposed flux detectors are serially connected to each other and have one flux detector associated with each magnetoelastic band and arranged to null out any static magnetic field such as the earth""s magnetic field. A triangular wave is applied to one end of each pair of saturable core magnetic flux detectors. A triangular wave is used because it will induce a current only odd harmonic constant voltage across the array until the array current saturates the detectors. A pair of differential amplifiers connected to each pair of serially connected flux detectors outputs a signal corresponding to the second harmonic of the triangular wave resulting from energizing the pair of saturable core flux detectors. The outputs from each pair of differential amplifiers are summed to produce an amplified output signal. The output signal is fed back to an offset amplifier to correct a reference signal being applied to the opposite ends of the pair of serially connected, saturable-core, magnetic flux detectors. An electronic control controls the frequency and pulse width at which the square wave is being generated and actuates the differential amplifiers to detect the second harmonic of the resultant signal. The torque sensor further includes an integrator connected between the output of each differential amplifier back to a summing node to periodically correct the output offset voltage of the differential amplifier to a predetermined value when the input to the amplifiers are grounded. The electronic control is further responsive to a malfunction of any of differential amplifiers to disable that amplifier and permit continued operation with reduced sensitivity. The electric control also includes means for varying the pulse width of the signals actuating the differential amplifiers to detect a second harmonic to change the band width and response rate of the torque sensor.
A first object of the invention is to provide a torque sensor having individual improved accuracy and reliability of magnetic flux measurement.
Another object of the invention is to provide automatic offset correction.
Another object of the invention is to provide an electronic control using digital electronics to control and synchronize the timing signals.
Still another object of the invention is the ability to vary the response rate of the sensing current to rapid changes in the detected torques.
A final object of the invention is to detect and compensate for sensor failures.
These and other objects of the invention will become more apparent from a reading detailed description of the invention in conjunction with the drawings.